In recent years, Bi has been contained instead of lead in many cases in copper alloy constituting a material for plumbing equipment, such as water valves, joints, etc., for example, in order to enhance properties including cuttability while preventing the elution of lead from the copper alloy. Though it is said that Bi only has relatively low toxicity, stringent lixiviation standards are provided also relative to Bi, and Bi-containing products not able to satisfy the lixiviation standards are present depending on lixiviation test methods and shapes and sizes of the Bi-containing products. In addition, lead lixiviation standards become more and more stringent and, for example, leadless copper alloy containing a trace of lead as an unavoidable impurity possibly fails to satisfy the lead lixiviation standards. Under these circumstances, it becomes important for plumbing equipment used for water that lead elution is prevented and further that Bi elution is suppressed.
As a technique for preventing the elution of a harmful substance of this kind, the lead elution prevention method of Patent Document 1, for example, has been known. Patent Document 1 discloses the removal of lead from the water-contacting portion of bronze or brass plumbing equipment and, to be specific, the water-contacting surface of the plumbing equipment is treated with 0.5 to 7 wt % of nitric acid to enable the elution of lead to tap water to be suppressed to a great extent. On the other hand, Patent Document 2 discloses a lead elution reduction treating method aiming at removing lead from the surface of lead-containing copper alloy through immersion of the copper alloy in cleaning liquid comprising alkaline etching liquid. Patent Document 3 discloses a regeneration treatment method that suggests from Table 2 a possibility of enabling Bi to be removed from a water-contacting portion in treating copper alloy with chemical grinding treatment liquids containing 27 wt % or lower nitric acid. In addition, the lead-free copper alloy includes that which does not intend to contain Bi in alloy, thereby inducing a technique for suppressing the elution of Bi.